The retina is a unique model for studying neuronal processing in general: the input is easily accessible to patterned physiological stimuli and the anatomy is organized and well-characterized. Retinal signal-processing will be investigated by studying the responses of cat retinal ganglion cells to patterns of light in space and time. These responses will be interpreted in terms of models of retinal processing that include not only the classical center and surround mechanisms, but also the nolinear subunit pathway of the Y cell, adaptation, and the contrast gain control. The models will be tested by their ability to predict responses to a wide range of visual stimuli. Patterns of light will be generated by a computer-controlled electronic display with high spatial and temporal resolution. Gangion cell activity will be monitored with microelectrodes inserted in the optic tracts of anaesthetized adult cats. A variety of mathematical techniques, including linear systems analysis and the sum-of-sinusoids method of nonlinear systems analysis, will be used to construct and analze physiological models. The immediate benefits of a full concise model of retinal processing are a clarification of the importance of the many retinal mechanisms that have been proposed, and an insight into the purpose of separation of visual information into the parallel X and Y channels. The long-term benefit of this project is a better understanding of information processing by the local circuits of the mammalian central nervous system.